qt信号时隙多线程死锁 [英] qt signal-slot multithreading deadlocks

问题描述

在我的代码中，工作线程向gui线程发出一个信号。信号和插槽通过Qt :: BlockingQueuedConnection连接。

In my code a worker thread emits a signal to gui thread. Signal and Slot are connected via Qt::BlockingQueuedConnection.

当 closeEvent 应用程序尝试停止工作

When during thecloseEvent application is trying to stop the worker thread and only then finishes the event.

它调用工作线程的函数：

It calls the function of worker thread:

void stop() {
  _isFinished = true;
  wait();
}

工作线程检查 _isFinished <

The worker thread in its turn checks _isFinished condition and if it is not set up then emit the signal.

成像以下情况

The worker            Gui Thread 
=================     =================
if (!_isFinished)     -----------------
-----------------     _isFinished = true;
-----------------     wait();
emit mySignal();      -----------------

显然，将被锁定 - 死锁。

Evidently, both threads would be locked - deadlock.

如果我添加一个互斥，那么你可以找到另一个死锁情况。当工作者锁定互斥量和gui线程将被阻塞。结果发出的信号将锁定工人。

If I add a mutex then you can find another deadlock situation. When the worker locks the mutex and the gui thread would be blocked. As a result the emitted signal will lock the worker.

我该如何处理？

推荐答案

这是我看到的情况。

主线程你不需要等待工人退出。您的 closeEvent 应该看起来像这样：

In your main thread you do not need to wait for worker to quit. Instead your closeEvent should look like this:

if (workerThread->isRunning())
{
    workerThread->stop();
    event->ignore();
}

要使这项工作，你还需要关闭主窗口，完成：

To make this work, you also need to close main window, when worker thread finishes:

connect(workerThread, SIGNAL(finished()), SLOT(close()));

最后，使用 _isFinished 所有其他变量在工作线程）应该发生在工作线程。您可以用一个简单的技巧实现它：

Finally, all manipulations with _isFinished (and all other variables in worker thread) should occur in worker thread. You can achieve it with a simple trick:

WorkerThread.h

public:
    void stop();

protected slots:
    void p_stop();

protected:
    QMutex mutex;

WorkerThread.cpp

void WorkerThread::stop()
{
    staticMetaObject.invokeMethod(this, "p_stop", Qt::QueuedConnection);
}

void WorkerThread::p_stop();
{
    QMutexLocker locker(&mutex);
    _isFinished = true;
}

这样可以避免死锁。

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